This invention relates to ultraviolet photoacoustic detection, and more particularly to ultraviolet photoacoustic zone detection.
Ozone is a strong oxidizing agent. An appropriate amount of ozone can be used to kill germs and bacteria and to remove toxic chemicals from fruits and vegetables. However, too much ozone can cause damage to the environment and cause harm to humans.
One method of detecting ozone is to intermix ozone with another gas and detect the chemiluminescence that results from the chemical reaction of the two gases. Another method is to expose ozone to ultraviolet light and measure the amount of reduction in the intensity of ultraviolet light at 254 nm. A higher concentration of ozone results in a greater absorption of the ultraviolet light. Such ultraviolet light can be generated from HgI lamps, which emit light having a wavelength of 253.7 nm.
When ultraviolet absorption is used for ozone detection, components in the air, such as water vapor and aromatic hydrocarbon compounds, may interfere the absorption process. Water does not absorb at 254 nm, but when the humidity is high, condensation of water vapor can block the passage of ultraviolet light and affect the accuracy of the measurement. Volatile aromatic compounds, such as benzene, toluene, xylene, and their derivatives that are generated by the combustion of fossil fuels, have absorption bands that overlaps with ozone at 254 nm. One way to overcome this is to use scrubbers to remove the aromatic compounds. Another way is to make a first ultraviolet absorption measurement, use scrubbers to remove the ozone, make another ultraviolet absorption measurement, and compare the difference in measurements.